1. Field of the Invention
The present invention relates to sheet feeding devices and image forming apparatuses, and in particular, relates to a sheet feeding device downsized without causing failure in sheet feeding and degradation in quality of printed matter and to an image forming apparatus downsized by being provided with the downsized sheet feeding device.
2. Description of the Related Art
Conventionally, image forming apparatuses, such as facsimile machines, copying machines, and laser beam printers, have been each provided with a sheet feeding device for feeding sheets, such as plain paper, coated paper, plastic sheets, and cloth, to an image forming portion in the image forming apparatus. In sheet feeding devices, it is very important to separate sheets one by one for their sending to image forming portions; therefore, to prevent multifeeding, i.e., feeding plural sheets from a sheet feeding device at one time, various sheet feeding methods have been proposed.
Moreover, in recent years, great importance has been placed on downsizing of sheet feeding devices as well as multifeeding prevention and stable sheet feeding. And further, with the widespread use of printers, facsimile machines and so on in ordinary households, it is demanded that image forming apparatuses be further downsized as well. In image forming apparatuses each provided with a sheet tray (sheet feeding cassette) in which sheets are stored, it is demanded that the dimension in the direction of the fitting of the sheet tray (hereinafter referred to as “the dimension of the fitting direction”) of the main body of the apparatus, in particular, do not exceed the dimension of the fitting direction of the sheet tray.
As an example of a sheet feeding device in which the dimension of the fitting direction of an image forming apparatus falls within the dimension of the fitting direction of a sheet tray, there is a sheet feeding device in which a sheet feeding roller is rotated forward and backward to separate sheets one by one (see Japanese Patent Laid-Open No. 5-147752). In such a sheet feeding device, when feeding sheets, the sheet feeding roller is rotated backward to begin with to feed the uppermost sheet in a sheet tray in the direction opposite to the direction of the sheet feeding. As a result, the uppermost sheet is bent once by being pressed on the back wall of the sheet tray for the separation of the sheet from the other sheets.
Thereafter, by rotating the sheet feeding roller forward, the sheet bent once goes up on a separation claw provided downstream in the direction of the sheet feeding of the sheet tray, whereby the sheets are separated one by one. By using such a mechanism, the function of feeding sheets separately can be provided within the dimension in the fitting direction of the sheet tray, and this enables the achievement of the dimension of the fitting direction of the image forming apparatus falling within the dimension of the fitting direction of the sheet tray.
Moreover, as another example, there is a sheet feeding device having a component that can be folded in a state of being stored with sheets, i.e., using a method in which sheets are put in the sheet tray in a state of being bent (see Japanese Patent Laid-Open No. 58-22224). Therefore, the provision of such a sheet feeding device enables the implementation of an image forming apparatus smaller than sheets used for image formation.
However, for such related art sheet feeding devices, in the case where, for example, a sheet is bent once to separate the sheet from the other sheets, it is necessary to provide a space for bending sheets above the sheet tray, and thus the height of the device increases. In the case where sheets are put in the sheet tray in a state of being curved, when the sheets have been held curved for a long time period, there is a possibility that the sheets curve at all times at their bent portions. Therefore, the feeding of such sheets curving at all times causes problems such as sheet feeding failures (paper jams, etc.) and transfer failures at the times of the transfer of an image onto sheets. And further, there is a possibility that only part of printed matter on which an image has been formed curves at all times, and thus a problem arises that the quality of the printed matter degrades.
In view of the present circumstances, the present invention provides a sheet feeding device capable of preventing the occurrence of failure in sheet feeding and degradation in quality of printed matter with downsizing achieved and an image forming apparatus provided with the downsized sheet feeding device.